1. Field of the Invention
The present invention relates to an electromagnetic flow-rate measurement system which is configured using electromagnetic flowmeters capable of measuring the flow of a conductive fluid.
2. Description of the Related Art
One of the pieces of measurement apparatus used for measuring the flow of conductive fluids is the electromagnetic flowmeter, the high degree of accuracy and durability of which has led to its wide adoption for use in industry.
FIG. 1 shows an example of the configuration of an electromagnetic flowmeter for industrial use.
The electromagnetic flowmeter shown in this drawing comprises a detector 1 and a converter 2. The detector 1 has a pair of electrodes 4a, 4b on the internal wall of the measurement pipe 3 through which the conductive fluid which is to be measured is passed, and a flow-rate measurement coil 5 located on the exterior of the measurement pipe 3 impresses a magnetic field on the fluid in a direction which intersects at right-angles the line along which the electrodes 4a, 4b face each other. The converter 2 converts the electromotive force which is generated between the electrodes 4a, 4b into voltage signals in an amplifier 6, and outputs them from an output circuit 8 via a sampling circuit 7. A switch 10 serves to switch between constant-current sources 9a, 9b, thus allowing an alternating current to flow to the flow-rate measurement coil for the purpose of excitation. The switching of the switch 10 is controlled by a exciting signal which is generated by a timing circuit 11 in synchronisation with a sampling signal from the sampling circuit 7.
FIG. 2 illustrates the timing of the above-mentioned electromagnetic flowmeter.
Control of the switch 10 by means of the exciting signal illustrated in this drawing allows the alternating current to flow to the exciting coil 5, and the electromotive force generated between the electrodes 4 in accordance with the flow-rate of the fluid which is to be measured is amplified by the amplifier 6. The output of this amplifier 6 is sampled when stable, and a flow-rate signal is transmitted from the output circuit 8.
Another example of a device which measures the flow-rate of a fluid in the same way as an electromagnetic flowmeter is the water meter which measures the amount of water consumed for household use. Recent demand for the rationalisation of meter-reading and a reduction in the number of meters which are difficult to read has led to the popularisation of centralised and mass meter-reading, where meters are read from a distance by electrical or magnetic means.
If the industrial electromagnetic flowmeter could be adapted to use with the household water meter, it would be possible to implement a high-precision remote centralised meter-reading system. However, in practice there are a number of factors which have prevented the adaption of the electromagnetic flowmeter to use with household water meters. Some of the reasons which may be adduced are as follows. There has been a problem in that the faintness of the electromotive force (flow-rate signal) generated between the electrodes 4a, 4b has necessitated a complicated configuration of circuits (sampling circuit 7, output circuit 8 etc.) in order to process the signal in the converter 2. Another problem has been the high cost involved in providing the electrical energy to generate an alternating magnetic field by means of the flow-rate measurement coil 5, and the cost of the exciting circuit comprising the constant-current sources 9a, 9b and the switch 10. Yet another problem has been the increased cost of power consumption running to several watts as compared with other types of mechanical water meter. Finally, it has been necessary to renew wiring and other equipment because the detector 1 normally requires an external power source.
Recent developments in electronics technology have succeeded in facilitating signal processing on a cheaper and smaller scale, but the continued need for an exciting circuit and wiring to supply the required electric power mean that problems of size and expense still remain.
Thus, any attempts hitherto to construct a remote centralised meter-reading system or other flow-rate measurement system by adapting electromagnetic flowmeters to use with household water meters have been fraught with problems size and expense resulting from the need to provide the exciting circuit and wiring to supply the required electric power.